Control system for a reaction process system

ABSTRACT

Control system for optimizing and stabilizing consumption of the reactants of a reaction process system. The control system comprises a system control means which receives system condition signals from the reaction process system and which generates adjustment signals for controlling the reaction process system. One of the system condition signals is the amount of consumption of an uncontrollable reactant being supplied to the system. The system control means will generate a signal which is proportional to the uncontrollable reactant consumption signal received to control the severity of reaction within a reactor in the system. Another signal received by the control system is an index indicative of conversion and material balance of the system. In a preferred embodiment this particular signal represents the level of the bottoms in a fractionator column. The control means has computer means for computing the change of this index with respect to time and for determining a parameter of comparison whose value is a function of the value of this index. Comparator means compares the actual rate of change of the index with the parameter of comparison and generates a signal for activating controller means in the reaction system. Comparator means is also provided to compare the index with limits of deviation and for generating signals for activating controller means in the reaction process system.

United States Patent Sayles et al.

CONTROL SYSTEM FOR A REACTION PROCESS SYSTEM Inventors: John H. Sayles,Arlington Heights; Allen L. lekar, Brookfield, both of III.

Universal Oil Products Company, Des Plaines, lll.

Filed: July 6, 1972 Appl. No.: 269,377

Related US. Application Data Continuation-impart of Ser. No. 160,022,July 6, 1971.

[73] Assignee:

us. 01...... 235115142, 208/DIG. 1, 235/1501 1m. 01. G06g 7/5s Field ofSearch 235/1501, 151.1,

235/15112; 208/DIG. 1,308, 106, 113

References Cited UNITED STATES PATENTS 2/l970 Urban 235/l5l.l2 X

3/1972 Bajek et al... 235/l5l.l2 X 4/1972 Putman 235/15L12 X PrimaryExaminer-Joseph F. Ruggiero Attorney-James R. Hoatson, Jr. et al.

[ 1 July 24, 1973 [5 7] ABSTRACT Control system for optimizing andstabilizing consumption of the reactants of a reaction process system.The control system comprises a system control means which receivessystem condition signals from the reaction process system and whichgenerates adjustment signals for controlling the reaction processsystem. One of the system condition signals is the amount of consumptionof an uncontrollable reactant being supplied to the system. The systemcontrol means will generate a signal which is proportional to theuncontrollable reactant consumption signal received to control theseverity of reaction within a reactor in the system. Another signalreceived by the control system is an index indicative of conversion andmaterial balance of the system. In a preferred embodiment thisparticular signal represents the level of the bottoms in a fractionatorcolumn. The control means has computer means for computing the change ofthis index with respect to time and for determining a parameter ofcomparison whose value is a function of the value of this index.Comparator means compares the actual rate of change of the index withthe parameter of comparison and generates a signal for activatingcontroller means in the reaction system. Comparator means is alsoprovided to compare the index with limits of deviation and forgenerating signals for activating controller means in the reactionprocess system.

16 Claims, 3 Drawing Figures CONTROL SYSTEM FOR A REACTION PROCESSSYSTEM This application is a continuation-in-part of our copendingapplication Ser. No. 160,022 filed July 6, l97l.

BACKGROUND OF THE INVENTION The present invention relates to a controlsystem for a reaction system wherein at least two reactants areutilized, one being an uncontrollable and varying supply. In thepetroleum refinery business, many processes fall into this category.That is, they require at least two reactants and of one of those may bein an uncontrollable and varying supply. Usually this occurs when one ofthe reactants is the product of other independent process of therefinery. For example, in a reforming process there is generally a netgain in hydrogen in the effluent. This hydrogen may be utilized inanother part of the plant such as in the hydrocracking of crude oil toproduce gasoline components. Depending upon the particular productionschedules of a refinery there may occur the possibility that lesshydrogen is produced by reforming than can be used by the hydrocrackingprocess. If this is the case, the hydrocracking process is hydrogenlimited. For economic purposes it is desirable to use all the hydrogenavailable. As the supply of hydrogen varies, readjustment of theoperating conditions of the hydrocracking unit is necessitated. This isa very difficult task for process operators to efficiently andconsistently proceed with and generally if done manually will result inthe venting of much hydrogen and thus the loss of potential profit fromthe hydrocracking unit.

SUMMARY OF THE INVENTION Thus, it is a principal object of thisinvention to provide for a control system for a reaction process systemwhich fully utilizes a reactant that is in an uncontrollable, varyingand limited supply.

Another object of this invention is to provide for a control system fora hydrocracking unit wherein hydrogen is in uncontrollable, varying andlimited supply and wherein such hydrogen is utilized to the maximumextent possible.

Another object of this invention is to maximize the amount of the secondreactant which is processed in combination with the reactant which isonly available in an uncontrollable, varying and limited supply.

A still further object of this invention is to simultaneously accomplishthe maximum utilization of the aforesaid reactants.

In a broad aspect, the present invention provides for acontrol systemfor a reaction process system having at least one reactor with inletmeans for introducing at least two reactants therein, one being inuncontrollable and varying supply and the second being in controllablesupply. The reaction process system would have, or course, outlet meansfor discharging the reactor effluent therefrom which broadly may includeseparators, fractionators, and the like. The control system is designedfor optimizing and stabilizing the consumption of the reactants and itmaintains an index indicative of conversion and material balance of thesystem within predetermined limits of deviation. This index willcomprise a factor which indicates the percentage of conversion and theamount of controllable reactant being converted. The control system willcomprise (a) first regulating means connected to the inlet means forregulating the supply of the controllable reactant; (b) secondregulating means connecting to said reactor for regulating the severityof reaction therein; (c) first sensing means connected to said reactionprocess system for generating a signal representative of the amount ofcontrollable reactant being supplied to the reactor; (d) second sensingmeans connecting to said reaction process system for generating a signalrepresentative of the severity of the reaction therein; (e) thirdsensing means connecting to said reaction process system for generatinga signal representative of the index indicative of conversion andmaterial balance of the system, (f) fourth sensing means connecting tosaid reaction process system for generating a signal representative ofthe amount of consumption of uncontrollable reactant being supplied tosaid reactor; (g) first controller means connecting to said firstregulating means for controlling the regulation thereof; (h) secondcontroller means connecting to said second regulating means forcontrolling the regulation thereof; and, (i) system control meansconnecting to said sensing means and to said controller means forreceiving said generated signals and for generating adjustment signalsfor controlling said reactor system. The system control means willinclude (l) first computer means for determining changes in the signalrepresentative of the amount of consumption of the uncontrollablereactant being supplied to said system and for generating an adjustmentsignal proportional to the changes for activating the second controllermeans to control the severity of reaction. Thus, the severity ofreaction will be determined by the amount of uncontrollable reactantbeing consumed and will be adjusted to consume maximum amounts of theuncontrollable reactant.

in a preferred embodiment this aspect of the system control means willbe generated by digital computer means and the computer means will storea digital representation of a reference signal representing the normalamount of consumption of uncontrollable reactant being supplied to thereactor.

Preferably, the system control means will scan the fourth sensing meansand measure the amount of consumption of the uncontrollable reactant atpredetermined intervals of time. lt will then generate an adjustmentsignal whose magnitude is proportional to the sum of: a componentproportional to the difference between the quantities resulting fromsubtraction of the two most recent readings and the reference signal; acomponent proportional to the sum of the differences between referencesignal and at least the three most recent readings; and a componentproportional to the sum of the differences between consecutive readingsmeasured including at least five differences between the most recentmeasurements.

The system control means will further comprise a second computer meansfor computing the change of the index with respect to time and fordetermining a parameter of comparison whose value is the function of thevalue of the index. Also included will be the first comparator means forcomparing the rate of change of the index with the parameter ofcomparison and for generating a signal for activating the firstcontroller means in response to this comparison. A second comparatormeans is also included for comparing the actual value of the index withthe limits of deviation and for generating a signal for activating thefirst controller means in response to such comparison. Preferably, thecomparator means will also generate a signal to the second controllermeans whose magnitude is proportional to the signal to the firstcontroller means. The magnitude of the adjustment signal made by thefirst comparator means to the first controller means is proportional tothe rate of change of the index.

Preferably, when the value of the index lies beyond the limits and whenthe direction of the change of the index with respect to time indicatesthat the index will continue to depart from the limits, the comparatormeans will generate a signal for the first controller means whosemagnitude is directly proportional to the change in the index withrespect to time and also including components to reverse the trend ofthe index. Components to reverse the trend may include a constant addedto the rate component to turn the trend of values and not merely tolevel it out. It is noted that this decision to make a correction is notmade unless the value is outside of the limits.

The parameter of comparison determined by said second computer meanswill comprise a first variable parameter whose value is given by theabsolute value of the difference between the measured value of the indexand the more proximate limit, with respect to time, and when the changeof the index with respect to time exceeds this first variable parameter,the first comparator means will generate a signal to said firstcontroller means. This signal is proportional to the change in the valueof the index with respect to time. Again preferably the first comparatormeans will also generate a signal to the second controller meansproportional to the signal to the first controller means. It is notedthat the magnitude of this correction can be variable depending upon thevalue of the proportionality constant selected.

When the value of the index lies within the limits and when the changeof the index with respect to time exceeds the first variable parameterand when the index is approaching the more proximate limit, thecomparator means will generate a signal to the first controller means,the generated signal being proportional to the change in the index withrespect to time and including components to reverse the trend of thevalue, e.g., a constant.

If the absolute value of the change in index with respect to timeexceeds the first variable parameter a correction will always be made.Preferably, a second variable parameter is used to determine anothercircumstance when the correction output will insure a trend reversal.The second variable parameter is given by the absolute value of: thedifference between the measured value of the desired property and themore distant limit, with respect to time. When the absolute value of thechange of the index with respect to time exceeds the second variableparaameter, the output is always computed so the trend reversal occurs.

It is noted that the present invention issues two types of correction.One is based on the amount of consump-' tion of the uncontrollablereactant and is proportional to this amount. This correction signaladjusts the severity of reaction and thus can control the severity tochange consumption of the uncontrollable reactant within relativelyshort time periods. When this occurs a change of the controllablereactant is generally required to react with the uncontrollablereactant. The control of the controllable reactant is determined by thesecond computer means. That computer means only issues a correction oradjustment signal which is proportional to the rate of change of theindex measured. The magnitude of the error between the actual value ofthe index and the desired value of the index in no way influences thevalue of the correction action in the same manner as the standardproportional controller as far as control of controllable reactant.

It is only the fact that an error exists rather than its magnitude whichinfluences the second computer means of the present control system.Another unique feature of the invention is that, the time sequence inwhich the correction action generated by the second computer means is avariable quantity and is also controlled by the rate of change of theindex.

The present invention therefore differs from the prior art controlsystem in that it provides for a correction whose magnitude isproportional only to the rate of change of the measured index, and inaddition with the control action timing also being a function of therate of change of the index.

The present control system is thus less affected by lag time than theproportional only, proportional plus reset etc. type of controller. Anadditional improvement is the use of a variable parameter which is afunction of the instantaneous value of the variable itself. Thus thecontrol system through the second computer means makes correction moveswhen the rate of change of an index exceed the variable parameter ofcomparison. Since the parameter of comparison is always changing in itsrelationship to the value of the index measured, the system itselfdetermines when a control adjustment is needed. This is obviously animprovement over a fixed time interval to make corrections. It also willmake corrections when the value of the index is beyond predeterminedlimits of deviation and is continuing to depart from such limits. Thusthe essence of the present invention is the use of computer means tofirst compute a change in severity necessary to fully utilize a limiteduncontrollable varying supply of. reactant and to use a derivativefunction of an index indicative of conversion and material balance toaccomplish both the magnitude and timing of corrections as determined bythe function of the instantaneous value of the index to control the flowof the controllable reactant.

Although the broad embodiment of this invention may utilize analoguemeans to generate the time as well as the type of correction, digitalmeans is also contemplated.

The reaction process system is directly applicable to hydrocarboncracking processes wherein the uncontrollable reactant compriseshydrogen and wherein the reaction process system further comprises apressurized liquid-vapor phase separation means connected to thedownstream side of the reactor for separating any unreacted hydrogen ina gaseous phase from the effluent of the reactor, and fractionationmeans connected downstream from the liquid end of said separation meansfor separating in a liquid phase any unreated controllable reactant fromthe liquid effluent, and wherein the first regulation means includesmeans for recycling from the fractionation means unreacted controllablereactant to said reactor and wherein unreacted hydrogen is recycled fromsaid separation means to said reactor. In this preferred embodiment thethird sensing means comprises level indicating means connected to thefractionation means for generating a signal representing the level ofthe bottoms in said separation means. The level thus serves as the indexindicative of conversion and material balance of the system. In otherwords, any change in level will indicate two things, that is, thepercent of conversion and/or the material balance of the system.Assuming that the percent of conversion is constant, any change in thelevel in the fractionation means will indicate a net change in thecontrollable reactant put into the system. If the net change ofcontrollable reactant is constant then any change in the level in thefractionation means will indicate a change in the percent of conversionof the reactor. In this embodiment the amount of consumption of theuncontrollable reactant hydrogen is preferably determined by pressureindicating means connected to the separation means which generates apressure signal therein. Change in temperature in the reaction zoneusually indicates change in severity of reaction. Thus, preferably thesecond sensing means comprises temperature sensing means connected tothe reactor for generating a signal representing temperature therein.

This system is a distinctly new departure from previous controlstrategies primarily in the concept of maximizing fresh feed rate as theH supply varies. It is also new in that both fractionation level andseparator pressure are maintained at set points while simultaneouslymaintaining the unit in feed-hydrogen balance at 100 percent conversion.

Reference to the accompanying drawing and the following descriptionthereof will serve to illustrate with moreclarity the present inventionand how it relates to the refinery process of hydrocracking ahydrocarbon.

DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is a schematicalillustration of a hydrocracking reaction process system utilizing thecontrol system of this present invention.

FIG. 2 of the drawing is a block flow diagram of one aspect of thecontrol system.

FIG. 3 of the drawing shows schematically a series of curves whichrepresent changing level and correction moves made by the controlsystem.

Reference is now made to FIG. 1 of the drawing where there is shown areactor having two catalytically active reaction zones 13 and 14therein. The zones comprise catalyst materials suitable for the hydrocracking of the hydrocarbon supported in a conventional manner suchas by perforate plate members and the like. An inlet line 11 is providedon the top or reaction chamber 10 and an outlet line 12 is provided onthe bottom of the reactor. The feedstock to the reaction chamber 10 isfirst introduced via conduit 43 into a preheater 15 which has heatexchange coils 16 disposed therein. The feed is heated by burners (notshown) supplied by fuel from fuel line 20. The amount of fuel suppliedis controlled by control valve 21. The amount of feed supplied throughline 43 is regulated by control valve 49 in line 43. Hydrogen isintroduced into the system as make-up hydrogen through line 1 whichconnects to outlet line 12 of the reactor. The hydrogen introduced intoline 12 is separated in a liquid-vapor phase separator 30 operating atan elevated pressure. From the separator 30 the hydrogen passes via line37 through a compressor 36 and to line 43. A quench hydrogen stream isintroduced into reaction chamber 10 downstream of the first bed via line33. The amount of quenching is regulated by control valve 38 in line 33.

A hydrogen vent line 34 and a control valve 35 is provided in hydrogenrecycle line 37 to vent off any excess hydrogen. Liquid effluent fromseparator 30 is passed through line 31 to fractionator 40 wherein thevarious components of the efiluent are fractionated. The overhead vaporgasoline components are removed via line 42, and the liquid gasolinecomponents are removed via line 41. The bottoms collected in the lowerpart of the fractionator 40 comprise fresh and recycle feed which ispumped to the reactor 10 via pump 48. Fresh feed is introduced into thefractionator via line 46 to first remove light ends although fresh feedmay be introduced into line 43. The control of feed through line 46 isregulated by control valve 47. Any excess recycle feed which cannot beused in the system may be removed via line 44. The removal of excessfeed is regulated by control valve 45.

The basic element of the control system for this reaction process systemis a system control means 100. System control means receives generatedsignals derived from various monitors or sensors in the system andgenerates adjustment signals to various controllers in the system tothus control the reactor system. A first signal used by the systemcontrol means is determined by a first sensing means connected to theinlet of the reactor which generates a signal representative of theamount of controllable reactant being supplied to the reactor. Thesensing means is schematically represented by an orifice 166 placed inline 43 and connected to a flow indicator-controller 165. A flow signalis generated by flow indicator-controller 165 via transmitting line 168to system control means 100.

The reaction severity of reactor 10 is preferably determined by theinlet temperatures as well as the outlet temperatures of the catalystzones. Thus, there is provided temperature indicators 101, 104, 111 and114 connected to the inlet of zone 13, the outlet of zone 13, the inletof zone 14 and the outlet of zone 14 respectively. Devices 101 and 104also serve as controllers with adjustable set points, although, it isalso contemplated that the controller aspects of the present inventionbe internal to the system control means, as distinguished from the useof external controllers shown in the drawing. The actual temperaturesensing devices may include conventional thermocouples and the likeplaced in convenient locations of the reactor. The temperature indicatordevices generate electrical signals, which are transmitted viatransmitting lines 102, 105 112 and 115 to system control means 100.

The flow of make-up hydrogen passing through line 1 is detected by anorifice and a flow indicating device 131 generates and transmits asignal via line 132 to the system control means 100. A pressureindicatorcontroller 121 is connected to line 37 and transmits a pressuresignal to the system control means 100 via transmitting line 122 andactivates control valve 35 via line 129. The amount of flow of freshfeed is detected through orifice 146 in line 46 and the signal istransmitted by flow detector-controller 147 via line to the systemcontrol means 100. The flow of any excess bottoms through line 44 ismeasured through orifice 156 and a signal is transmitted via flowindicator-controller via transmitting line 158 to system control means100, and the flow is controlled by control valve 45 which is connectedto controller 155 via line 190. The flow of fuel 'to heater 15 iscontrolled by a flow indicator-controller 107 having a variable setpoint connected to an orifice 106, via line 110. Flowindicatorcontroller 107 is connected to control valve 21 viatransmitting line It. The set point of flow indicatorcontroller 107 isregulated by the temperature indicator-controller 101 which generates asignal to the flow controller via transmitting line 108. In this mannerthe severity of reaction can be controlled by changing the flow of fuelto heater 15. The severity of reaction can be controlled on downstreamreaction zone 14 independently by regulating the amount of quenchhydrogen through line 33 via control valve 38. The flow through line 33is controlled via a flow indicatorcontroller 117 which has the variableset point controlled by the temperature indicator-controller 1 11 viatransmitting line 118. Flow controller 117 is connected to an orifice116 via line 120.

The level of the bottoms in the fractionator 40 is sensed through aconventional level sensing means and the signal is transmitted to thesystem control means 100 by a level indicator 141 via transmitting line142.

The hydrocracking system is operating at best efficiency when all of thehydrogen flowing through line 1 into the system is consumed and nobottoms are being removed through line 44. Thus, no hydrogen would bevented through line 34. The first condition where all hydrogen is beingconsumed would be manifested by a normal operating pressure of theseparator 30. This pressure is hereinafter referred to as the referencepressure, P of the separator 30 and any deviation in this pressure issensed in the pressure indicator-controller 121. The pressureindicator-controller 121 does not activate the valve 35 unless an upperlimit in pressure is reached. The control of valve 35 may be madeindependent of any control signal derived from the system control means100. However, the pressure signal derived from the pressure indicatingdevice 121 will indicate changes in the hydrogen delivered through line1 and consumed in the reaction process carried on in the reactor 10. Inother words, given a situation where the hydrogen make-up supply remainsconstant, a change in pressure indicated by pressure sensing means 121will indicate there is a change in hydrogen consumption in the reactor10. The pressure signal will also indicate under constant reactionconditions whether or not more hydrogen is being introduced in thissystem via line 1 which also indicates a change in available hydrogenconsumed. That is, under constant reactor conditions if more hydrogen isbeing introduced through line 1 the pressure in separator 30 willincrease. Thus, the pressure signal from the sensing device 121 willgenerate a signal representative of the amount of consumption of theuncontrollable reactant hydrogen being supplied to the reactor. Itconsequently represents the fourth sensing means referred to in theSummary of Invention. This signal is utilized by the system controlmeans for generating a signal for controlling the reaction severity inthe reactor to thus utilize optimum amounts of hydrogen in the reactionprocess.

The reaction severity in the reactor may be controlled in variousmanners. One embodiment merely utilizes temperature controllers havinginlet temperature set points. In other words, temperatureindicatorcontrollers 101 and 111 would have controllable inlettemperature set points which would be changed by electrical signalimpulses generated via the system control means through transmittinglines 103 and 113 respectively. By way of example, if an increase inseverity were called for by reason of an increase of pressure inseparator 30 the system control means would generate signals to thetemperature indicator-controllers 101 and 111 to change their respectiveset points. Thus, temperature recorder 101 would adjust the set point offlow controller 107 via transmitting line 108 which would adjust valve21 to introduce a change in fuel to heater 15 which would change thetemperature of the incoming feed thorugh line 43. At the same timetemperature indicator-controller 111 would adjust the set point of flowcontroller 117 to change the amount of hydrogen quench via valve 38 inline 33.

Since it is not always true that the inlet conditions of reaction bedsaccurately indicate the severity of reaction in a reaction zone, arefinement utilizes the differential temperatures of the catalyst bedsto maintain a given severity. in other words, the set points ofcontrollers 101 and 111 may be defined to include the temperaturedifferential across each bed in the reactor.

A variation of the differential temperature set point concept is in theuse of a signal derived from the function of the outlet temperature ofeach bed to control the inlet temperature set points of the inlettemperature controllers. In this embodiment outlet temperature setpoints of each reaction zone would be stored in the system controlmeans. The system control means would compute an adjustment signal forthe set points of the inlet temperature controllers. This signal ispreferably made equal to the sum of two components, the first componentbeing proportional to the difference between the products resulting fromthe subtraction of each of the two most recent outlet temperaturesmeasured from the outlet temperature set point corresponding to thecatalyst bed in question. The second component is proportional to anintegral function of the deviation of the outlet temperature from theoutlet temperature set point. This component is proportional to the sumof the differences between the outlet temperature set point and at leastthree most recent outlet temperatures measured. Preferably, the fivemost recent outlet temperatures measured are used in this computation. Acomponent proportional to a differential function of the outlettemperature is not normally considered necessary or desirable. incomputing the change in magnitude of the temperature control signalsfrom the system control means to the temperature control means, themagnitude of the amount of change in the temperature control signal maybe expressed, in a preferred form, by an equation as follows:

(Tc- 19] n=0 In this equation X-, is the change in magnitude of thetemperature control signal derived by the system control means andtransmitted to the set point of the temperature controller at the inletof each bed. K, is a constant applied to the temperature function. T, isthe outlet temperature set point of the catalyst bed considered, T,, isthe actual outlet bed temperature measured during scan member n and K isa constant to be applied to the integral function of outlet temperature.When utilizing this form of temperature control any pressure controlsignal from the system control means would adjust the outlet temperatureset points.

The first component in this equation is normally the most significant indetermining the magnitude of the signal X That is, the differencebetween the deviations of each of the two most recent outlettemperatures measured from the outlet set point is the most significantfactor in determining the magnitude of change in the temperature controlsignal X Preferably, X must first reach a certain minimum value beforeit indicates a change in the inlet and outlet temperature. This is topreclude unnecessary temperature adjustment resulting from outlettemperature measurement deviations which are within the allowable airlimits of the outlet temperature measurement device of the temperaturecontroller means.

Regardless of the particular type of temperature control utilized forcontrol of the reactant severity, it is important to note that thepresent invention provides that ultimately the control of severity isdetermined by the amount of consumption of the uncontrollable reactant,hydrogen, being supplied to the system. The system control means hasfirst computer means for generating an adjustment signal proportional tothe changes in this value. in this preferred embodiment the pressuresignal derived by pressure sensing means 121 is used to determine theconsumption of hydrogen supplied to the reaction system. Preferably thesystem control means comprises digital computer means which stores adigital representation of a reference signal representing a normalamount of consumption of hydrogen being supplied to the reactor. Thesystem control means scans the pressure sensing means and measurespressure at predetermined intervals of time and generates an adjustmentsignal through the inlet temperature controllers uitlized, orinteriorally adjusts the outlet temperature set points if the alternateform of temperature control is utilized. This adjustment signal ispreferably proportional to the sum of a component proportional to thedifference between quantities resulting from subtraction of the mostrecent pressure reading and the reference pressure reading; a componentproportional to the sum of the differences between the referencepressure and at least the three most recent pressure readings; and acomponent proportional to the sum of the difference between consecutivepressure readings measured including at least five differences betweenthe most recent pressure readings. Of course, more pressure reading maybe utilized in the last component. This statement may be represented bythe following equation:

In the equation the term X, is the pressure control signal generated bythe system control means to operate the temperature controllers byadjusting the temperature set points of the temperature controllersutilized. K, is a constant applied to the pressure function, P is thenormal operating pressure, P, is the actual pressure measurement takenduring a scan number n, K is a constant applied to the integral functionof pressure and K is a constant applied to the differential function ofpressure. In the computation of X,,, the first component is normally thelarge component in determinging the signal. That is, the componentproportional to the difference between the products resulting from thesubtraction of the two most recent pres sures measured from the normaloperating pressure is normally the most significant component indetermining X,,. As was true of the preferred form of severitymaintenance, once the magnitude of the pressure control signal to thetemperature control means has been determined, it is frequentlydesirable to arrange the system control means and the temperaturecontrol means so that an increment in the pressure control signal to thetemperature control means must achieve at least a minimum magnitudebefore the temperature control means is actuated thereby. This featureprevents unnecessary cycling of the reactor system due to minor signalvariations from the pressure sensing means that lie within the tolerableand acceptable range of error of the pressure measurements.

From the foregoing it is seen that the system will be self adjusting toutilize all of the hydrogen being supplied to the system. However, withan increase in severity, an increase in consumption of hydrogen willresult, and thus more of the feed introduced into the reactor viarecycle line 43 will be consumed in the process. The result of thisphenomena is that the level in the bottoms of the fractionator 40 willdecrease. Of course, if less hydrogen is being introduced into thesystem the pressure control means will reduce the severity of thereaction in reactor 10 and thus the bottoms of the fractionator willincrease in level. The level of the fractionator thus indicates theconversion and material balance of the system and may be used as indexto optimize and stabilize the consumption of the feed in line 43. It isobvious that if more feed is being consumed, more feed will have to beintroduced into the system via supply line 46 and more feed will have tobe introduced into the reactor via line 43. The control of the valves47- and 49 in lines 46 and 43 is done via flow indicatorcontrollers 147and 165 which have variable set points. Flow controllers 147 and 165receive adjustment signals via lines 148 and 167 from the system controlmeans to change their respective set points. The flow controllers inturn close or open thier respective valves via transmitting lines 149and 169. If an overflow situation occurs, flow controller receives asignal from the system control means 100 via line 157 to release bottomsfrom the fractionator via conduit 44.

The adjustment signal for the flow control valves is determined by thesystem control means which will include computer means for computing thechange of level with respect to time and also for computing a variableparameter of comparison. The system control means may include ananalogue computer, a digital computer with analoque conversion means, ora completely digital system. It must include means for computing thechange of the level of the bottoms in fractionator 40 with respect totime. The system control means will further comprise a first comparatormeans for comparing the rate of change of the level with respect to timewith the parameter of comparison and for generating a signal to activatethe flow control means in response to this comparison. A secondcomparator means is included in the system control means for comparingthe actual value of the level with predetennined limits of deviation andfor generating an adjustment signal in response to this comparison. Thesystem control means will of course have means for storing the values ofthe limits of the level.

When the level lies beyond the limits and when the change of the levelwith respect to time indicates that the value will continue to departfrom such limits, the comparator means will generate an adjustmentsignal wherein N is the first variable parameter, L, is the value of thelevel, L, is the more proximate limit and At is the arbitrary timeperiod.

When the absolute value of the change of level with respect to timeexceeds the first parameter, (N), the comparator means will generate asignal to the controller means 147 and 165. The alteration made underthis circumstance is proportional to the change of the level withrespect to time. However, when the level lies within the limits and whenthe level is approaching the more proximate limit the correction willalso include a trend reversal signal.

The parameter of comparison may further comprise a second variableparameter whose value is given by the absolute value of: the differencebetween the mea sured level and the more distant limit, both withrespect to time. This statement may be represented by the formula:

M: At

where M is the second variable parameter, L, is the measured level, L,is the value of the more distant limit, and At is an arbitrary timeperiod. When the absolute value of the rate of change of level exceedsthis second variable parameter (M), the correction will also be computedso that a trend reversal occurs.

Preferably, the system control means will comprise a digital computerwhich will receive a signal from the level sensor, convert it to digitalcomponents and after determining proper signals for control, convertthem back to analogue signals for use by controller means 147 and 165.The digital computer will comprise clock means located therein that willperiodically scan incoming signals from the level sensing means 141 atpredetermined intervals of time. The computer will comprisedifferentiating means for computing the change of the value of thedesired property with respect to a predetermined time incrementcorresponding to at least one of the time intervals it scans. It willalso have storage means for storing values of the level as well as thevalues of predetermined limits.

A typical flow sheet for the control of the feed is shown in FIG. 2 ofthe drawing. The letter N corresponds to the first variable parameterwhose value is equal to the absolute value of the difference between thelevel and the more proximate limit; divided by the predetermined timeincrement. The letter M corresponds to the second variable parameterwhose value is computed to be equal to the absolute value of thedifference between the level and the more distant limit divided by thepredetermined time increment. AL/At is the change of level with respectto the time increment.

L, corresponds to the lower limit, L, corresponds to the upper limit, L,and L,, correspond to the values of the level of the present time and atthe time one increment earlier respectively. K is an arbitrary constantof proportionality. C is a constnat whose value will effect reversal oftrend. Reversal also can be effected by varying the proportionalityconstant. It is assumed that the second computer means has alreadycalculated M, N,AL/At and stored the quantities of L, and L, as well asthe lower limit L, and the upper limit L, and other informationnecessary to make decisions.

Referring to block A of FIG. 2 it is seen that the input of the absolutevalue of AL/At and the input M are compared in a circuit of the firstcomparator. If the absolute value of AL/At is greater than M, thecomparator will allow the generation of a correction signal proportionalto AL/At plus the constant which will help turn around the process. Ifthe absolute value of AL/At is less than or equal to M the logical flowwill go to block B of the second comparator where L, is compared withthe upper limit L If L, is greater than L,, the logical step is to seeif AL/At is increasing, which is done in block C of the first comparatorby the comparison of AL/At with 0. If ALIA! is equal to or greater than0 the comparator means allows the generation of a correction signalproportional to AL/At plus a constant. If AL/At is less then 0 than thenext logical step is block D. Also, if L, is less than or equal to theupper limit, the next logical step is block D of the second comparatorwhere L,, is compared with a lower limit L,. If L, is less than thelower limit the logical step is block E of the first comparator whereAL/At is compared with 0 again. If AL/At is equal to or less than 0 thecomparator means will allow the generation of a signal proportional toAL/At plus the constant. If AL/At is greater than 0, the next step shownis block F. Also, if L, is greater than or equal to the lower limit L,the next logical step is block F. In block F, the absolute value ofAL/At is compared with N; if the absolute value of AL/At is less than orequal to N, no correction is made. If the absolute value of AL/At isgreater than N, the next logical step is shown in block G where L, iscompared with the lower limits and the upper limits. If L, is greaterthan the lower limit and less than the upper limit the correction isproportional to AL/At plus a constant. If L,, is less than the lowerlimit or greater than the upper limit then the correction is merelyproportional to AL/At which is basically a line out correction.

In FIG. 3 there is shown various curves showing the positions L, and L,as well as calculated quantities N and M. It is noted that the slopefrom L, to L, is equal to AL/At if the space between the vertical linesis equal to At. It is seen that in example I, L, is greater than L, andAL/At is greater than or equal to 0. Thus, the correction move isproportional to AL/At plus a constant. ln example 2, L, is greater thanL, but AL/Az is less than 0. Furthermore, the absolute value of AL/At isless than N; therefore, no correction is needed. In curve No. 3, it isseen that L, is greater than L, but AL/At is less than 0. However, theabsolute value of AL/Az is greater than N and therefore a correctionoutput is needed. The absolute value of AL/At, however, is less than Mand L, is greater than the upper limit there greater than N and M;therefore the correction is proportional to AL/At plus a constant. Inexample the absolute value of AL/At is greater than N and the absolutevalue of AL/At is less than M. Typically, this would indicate that thecorrection should be the line out move without a constant added but C,,is greater than the lower limit and less than the upper limit andtherefore the constant is added to the correction and the correction isproportional to AL/At plus C. In example 6 the absolute value of AL/Atis less than N and M and L,, is within the limits; therefore nocorrection is made. In example 7 the absolute value of AL/At is greaterthan N but less than M and L,, lies within the limits. However, L isalso within the limits and therefore the correction is proportional toAL/At plus the constant. In example 8, L, is less than the lower limitbut AL/At is greater than 0 so no correction is made on this account.However, the absolute value of AL/At is greater than M and thus greaterthan N so the correction is proportional to AL/At plus the constant. Inexample 9, L is less than the lower limit but AL/At is greater than 0 sono correction is made on thqt account. The absolute value of AL/At isgreater than N but less than M; therefore, the correction isproportional to AL/At with no turn around constant added. The correctionis merely a line out move. In example 10 the absolute value of AL/At isless than M and N but L, is less than the lower limit and AL/At is lessthan zero. Therefore a correction is called for proportional to AL/Atplus the turn around constant.

From the foregoing description it is seen that the advantage of thelevel control part of the system is that the correction moves are notmade constantly, nor are they made at predetermined intervals of time.The process is allowed to continue wihout correction unless the absolutevalue of the change in level with resepect to time is greater than N orif the value of the level L, is beyond the limits and continuing todepart from such limits. Thus, the moves are not merely timed moves butare made only when the value of the level and change of the level withrespect to time exceeds certain parameters. The correction iteslf isalways proportional to the rate of change of the level. When a turnaround move is necessary to make the level approach or stay within thelimits, a constant is added to the correction signal or a differentproportionality constant is utilized.

As mentioned before, the correction signal derived from the levelcontrol aspects of this invention is proportional to be the change inlevel with respect to time. The proportionality constant will vary withparicular applications and particular apparatus utilized. Typically, thesignal will be equal to X ==(K -K, K,) (dl/dt Where X F is the change inmagnitude of the level control signal, dl/dt is the rate of level changeper unit time, K is a temperature volume correction process liquids, Kconverts the change in level over a known time to an equivalentconversion value such as barrels per day, and K, is the proportionalityconstant which will depend on the frequency of change known to exist inthe particular vessel and the system. A constant C may be added to thischange when trend reversing situations are required. It is also possibleto introduce another proportionality constant K to reverse the trend.(The correction sign or of K, is dependent on whether an inflow oroutflow of material or energy from the chamber is controlled.)

The system of this invention is now complete. That is, the controlsystem will optimize and stabilize the consumption of the reactants andwill utilize maximum amounts -of uncontrollable hydrogen reaction.Consider the situation where no hydrogen is being vented from conduit34, the pressure in the separator 30 is maintaining a constant value,and no bottoms are being removed from line 44. Then, if a change isintroduced into the system by the introduction of more or less hydrogenthrough conduit 1, almost immediately the pressure indicator 121 willdetect a change in pressure in the separator 30 and transmit the signalto system control means where an adjustment signal is determined to beused by the temperature contollers of the reactor to adjust the severityof the reactor. A change in severity will mean that there is a change inconsumption of the liquid hydrocarbon feed flowing through conduit 43,which in turn means that the level within the fractionator 40 willchange. The level control aspects of this system are such that noadjustmemts will be made in introducing feed into the system unlessvariable parameters are exceeded or, unless, the level is continuing todepart from preexisting limits of deviation.

A further refinement of the control system of this invention providesfor a feed forward control of the reaction severity of the reactordependent on the level control of the flow of the liquid hydrocarbon. Inthis embodiment the system control means will, in addition tocontrolling the flow through conduit 43 and conduit 46 in response tolevel comparisons, adjust the severity of reaction through thetemperature controllers. This adjustment signal will be proportional tothe adjustment signal determined for the control of control valves 47and 49. This in effect is a feed forward signal to the reactor. Theadjustment signal may be represented by the following formula:

where X is the adjustment signal for the temperature controllers 101 and111 or 104 and 114, K is a proportionality constant empiricallydetermined by data derived from the reactor system, and X L is thecorrection signal determined by the level control aspects of this systemcontrol means 100. The reason for the feed forward control is to adjustthe severity of reaction resulting from a change in feed flow which, ifnot compensated for, will likely affect the consumption of hydrogen. Thepressure control aspects of the system control means will normally takecare of the affect of hydrogen consumption by lowering the severity ofreaction but a feed forward control will make the response time shorterand thus negate or minimize the use of the pressure control aspects ofthis invention. When utilizing this particular refinement, it is alsopossible to introduce a proportionality constant into the X L formuladescribed above for control of the flow in conduits 43 and 46 to take inaccount the change in severity due to the feed forward control of thetemperature controllers. Thus, the formula for the change in flowthrough lines 43 and 46 may be written according to the followingformula:

where the additional porportionality constant is (l+K -K,) where K,, isthe feed forward proportionality constant used to control thetemperature controllers and where K; is a proportionality constant whichtakes into account the increase in reaction severity and eliminateschanges in level in the fractionator 40 due to changes in severityresulting from the feed forward adjustment signal.

It is evident that the control system of this present invention may beapplicable to many utilizations besides that which is illustrated inFIG. 1 of the drawing. The use of a two zone reactor should not belimiting upon the present invention for a single zone reactor, multiplereactors, as well as plurality zone reactors of more than two zones iscontemplated. Furthermore, the index indicating conversion and materialbalance may comprise signals derived from chromatographs, connected tothe resulting effluent and may include signals indicative of thematerial balance of the system as derived from the total flow in andtotal flow out of the system. Also it is possible to determine theamount of hydrogen consumed by other means than pressure sensing devicessuch as by hydrogen balance measurements. In this latter embodient aninitial correction to the reactor temperatures and feed rate could occurin a feed forward mode based on the change in hydrogen flow as sensed,followed by action of the control system in the manner previouslydescribed.

We claim as our invention:

1. In a reaction process system having at least one reactor with inletmeans for introducing at least two reactants, one being inuncontrollable and varying supply and the second being in a controllablesupply, and with outlet means for discharging the reactor effluenttherefrom, a control system for optimizing and stabilizing consumptionof the reactants which maintains an index indicative of conversion andmaterial balance of the system within predetermined limits of deviationocmprising in combination:

a. first regulating means connected to the inlet means for regulatingthe supply of the controllable reactant;

b. second regulating means connecting to said reactor for regulating theseverity of reaction therein;

c. first sensing means connected to said reaction process system forgenerating a signal representative of the amount of controllablereactant being supplied to the reactor;

d. second sensing means connecting to said reaction process system forgenerating a singal representative of the severity of the reactiontherein;

e. third sensing means connecting to said reaction process system forgenerating a signal representative of the index indicative of conversionand material balance of the system; fourth sensing means connecting tosaid reaction process system for generating a signal representative ofthe amount of consumption of uncontrollable reactant being supplied tosaid reactor;

g. first controller means connecting to said first regulating means forcontrolling the regulation thereof;

h. second controller means connecting to said second regulating meansfor controlling the regulation thereof; and,

i. system control means connecting to said sensing means and to saidcontroller means for receiving said generated signals and for generatingadjustment signals for controlling said reactor system, said systemcontrol means including: (1) first computer means for determiningchanges in the signal representative of the amount of consumption of theuncontrollable reactants being supplied to said system and forgenerating an adjustment signal proportional to the changes foractivating the second controller means to control the severity ofreaction, whereby optimum amounts of uncontrollable reactant may beconsumed; (2) second computer means for computing the change of saidindex with respect to time and for determining a parameter of comparisonwhose value is a function of the value of the index; (3) firstcomparator means for comparing the change of the index with respect totime with said parameter of comparison and for generating a signal foractivating said first controller means in response to said comparison;and, (4) second comparator means for comparing the actual value of theindex with the limits of deviation and for generating a singal foractivating said first controller means in response to said comparison.

2. The reaction process system of claim 1 wherein said second sensingmeans comprises temperature sensing means for determining temperatureconditions within said reactor, and wherein said second regulating meanscomprises means for regulating the temperature conditions within saidreactant.

3. The reaction process system of claim ll wherein:

a. said reactor comprises at least one reaction zone;

b. outlet temperature sensing means is connected to the outlet side ofsaid reaction zone for generating signals for said system control meansrepresentative of the outlet temperature of said reaction zone;

c. said second controller means comprises an inlet temperaturecontroller having a controllable set point;

d. said second regulating means comprises means for regulating thetemperature conditions within said reaction zone;

e. said system control means includes means for storing a contollableoutlet temperature set point, said outlet temperature set point beingadjusted in response to the signal generated by said first comparatormeans; and,

f. said system control means includes means for scanning the signalsgenerated by said outlet temperature sensing means at predeterminedintervals of time and for comparing said signals against said outlettemperature set point and for generating adjustment signals to adjustsaid inlet temperature controller set point, the magnitude of saidadjustable signal being equal to the sum of: a component proportional tothe difference betwen the products resulting from subtraction of each ofthe two most recent outlet temperatures measured from the outlettemperature set point and a component porportional to the sum of thedifferences between the aforesaid outlet temperature set point and atleast the three most recent outlet temperatures measured.

4. The reaction process system of claim 1 wherein:

a. said system control means includes means for storing a referencesignal representative of the normal amount of consumption ofuncontrollable reactant being supplied to said reactor;

b. said system control means includes means for scanning signalsgenerated by said fourth sensing means at predetermined intervals oftime and for comparing said signals against said reference signal andfor generating an adjustment signal to said second controller whosemagnitude is proportional to the sum of: a component porportional to thedifference between the quantities resulting from subtraction of the twomost recent readings of the amount of consumption of uncontrollablereactant and the reference reading; a component porportional to the sumof the differences between the reference reading and at least the threemost recent readings of the amount of consumption of uncontrollablereactant; and a component poroportional to the sum of the differencesbetween consecutive readings of the amount of consumption ofuncontrollable reactant including at least five differences between themost recent readings.

5. The reaction process system of claim 1 wherein when the index liesbeyond the limits, and when the direction of the change of the limitwith respect to time indicates that the index will continue to departfrom said limits, the comparator means will generate a singal for saidfirst controller means whose magnitude is directly porportional to thechange of the index with respect to time and also including componentsto reverse the trend of the index.

6. The reaction process system of claim 5 wherein said comparator meanswill also generate a signal to said second controller means whosemagnitude is proportional at the signal to said first controller means.

7. The reaction process system of claim 1 wherein the magnitude of theadjustment signal made by said first comparator means comprises a signalproportional to the change of the index with respect to time.

8. The reaction process system of claim 1 wherein said parameter ofcomparison comprises a first variable parameter whose value is given bythe absolute value of the difference between the measured value of theindex and the more proximate limit, with respect to time, and when thechange of the index with respect to time exceeds the first variableparameter, said first comparator means will generate an adjustmentsignal' to siad first controller means proportional to the change of theindex with respect to time.

9. The reaction process system of claim 8 wherein said first comparatormeans will also generate a signal to said second controller meansproportional to the adjustment signal to said first controller means.

10. The reaction process system of claim 8 wherein when the index lieswithin the limits and when the absolute value of the change of the indexwith respect to time exceeds the first variable parameter, and when theindex is apporaching the more proximate limit, the comparator means willgenerate a signal to said first controller means, the generated signalbeing proportional to the change of the index with respect to time andincluding components to reverse the trend of the value of the index.

11. The reaction process system of claim 8 wherein said parameter ofcomparison further comprises a second variable parameter whose value isgiven by the absolute value of: the difference between the index and themore distant limit, with respect to time, and when the absolute value ofthe change of the index with respect to time exceeds the aforesaidsecond variable parameter, said comparator means will generate a signalto said first controller means, the signal being proportional to thechange of the index with respect to time and including components toreverse the trend of the index.

12. The reaction process system of claim 1 wherein:

a. said reaction process system comprises a hydrocarbon cracking processwherein said uncontrollable reactant comprises hydrogen;

b. the reaction system further comprises a pressurized liquid-vaporphase separation means connected to the downstream side of said reactorfor separating any unreacted hydrogen in a gaseous phase from theeffluent of said reactor;

c. wherein fractionation means is connected donwstream form the liquidend of said separation means for separating any unreacted controllablereactant in a liquid phase from the liquid effluent;

d. said first regulation means includes means for recycling from saidfractionation means unreacted controllable reactant to said reactor;and,

e. means is connected to said reactor to said separation meansforrecycling hydrogen from said separation means to said reactor.

13. The reaction process system of claim 12 wherein said third sensingmeans comprises level indicating means connected to said fractionationmeans for generating a signal representative of the level of liquidbottoms in said fractionation means.

14. The reaction process system of claim 12 wherein said fourth sensingmeans comprises pressure indicating means connected to said separationmeans for generating a singal representative of the pressure therein.

15. The reaction process system of claim 12 wherein said second sensingmeans comprises temperature sensing means connected to said reactor forgenerating a signal representative of temperature conditions therein.

16. The reaction process system of claim 12 wherein said fourth sensingmeans comprises flow sensing means connecting to said reaction processfor generating a signal representative of the hydrogen consumption ofthe said reaction process.

1. In a reaction process system having at least one reactor with inletmeans for introducing at least two reactants, one being inuncontrollable and varying supply and the second being in a controllablesupply, and with outlet means for discharging the reactor effluenttherefrom, a control system for optimizing and stabilizing consumptionof the reactants which maintains an index indicative of conversion andmaterial balance of the system within predetermined limits of deviationocmprising in combination: a. first regulating means connected to theinlet means for regulating the supply of the controllable reactant; b.second regulating means connecting to said reactor for regulating theseverity of reaction therein; c. first sensing means connected to saidreaction process system for generating a signal representative of theamount of controllable reactant being supplied to the reactor; d. secondsensing means connecting to said reaction process system for generatinga singal representative of the severity of the reaction therein; e.third sensing means connecting to said reaction process system forgenerating a signal representative of the index indicative of conversionand material balance of the system; f. fourth sensing means connectingto said reaction process system for generating a signal representativeof the amount of consumption of uncontrollable reactant being suppliedto said reactor; g. first controller means connecting to said firstregulating means for controlling the regulation thereof; h. secondcontroller means connecting to said second regulating means forcontrolling the regulation thereof; and, i. system control meansconnecting to said sensing means and to said controller means forreceiving said generated signals and for generating adjustment signalsfor controlling said reactor system, said system control meansincluding: (1) first computer means for determining changes in thesignal representative of the amount of consumption of the uncontrollablereactants being supplied to said system and for generating an adjustmentsignal proportional to the changes for activating the second controllermeans to contRol the severity of reaction, whereby optimum amounts ofuncontrollable reactant may be consumed; (2) second computer means forcomputing the change of said index with respect to time and fordetermining a parameter of comparison whose value is a function of thevalue of the index; (3) first comparator means for comparing the changeof the index with respect to time with said parameter of comparison andfor generating a signal for activating said first controller means inresponse to said comparison; and, (4) second comparator means forcomparing the actual value of the index with the limits of deviation andfor generating a singal for activating said first controller means inresponse to said comparison.
 2. The reaction process system of claim 1wherein said second sensing means comprises temperature sensing meansfor determining temperature conditions within said reactor, and whereinsaid second regulating means comprises means for regulating thetemperature conditions within said reactant.
 3. The reaction processsystem of claim 1 wherein: a. said reactor comprises at least onereaction zone; b. outlet temperature sensing means is connected to theoutlet side of said reaction zone for generating signals for said systemcontrol means representative of the outlet temperature of said reactionzone; c. said second controller means comprises an inlet temperaturecontroller having a controllable set point; d. said second regulatingmeans comprises means for regulating the temperature conditions withinsaid reaction zone; e. said system control means includes means forstoring a contollable outlet temperature set point, said outlettemperature set point being adjusted in response to the signal generatedby said first comparator means; and, f. said system control meansincludes means for scanning the signals generated by said outlettemperature sensing means at predetermined intervals of time and forcomparing said signals against said outlet temperature set point and forgenerating adjustment signals to adjust said inlet temperaturecontroller set point, the magnitude of said adjustable signal beingequal to the sum of: a component proportional to the difference betwenthe products resulting from subtraction of each of the two most recentoutlet temperatures measured from the outlet temperature set point and acomponent porportional to the sum of the differences between theaforesaid outlet temperature set point and at least the three mostrecent outlet temperatures measured.
 4. The reaction process system ofclaim 1 wherein: a. said system control means includes means for storinga reference signal representative of the normal amount of consumption ofuncontrollable reactant being supplied to said reactor; b. said systemcontrol means includes means for scanning signals generated by saidfourth sensing means at predetermined intervals of time and forcomparing said signals against said reference signal and for generatingan adjustment signal to said second controller whose magnitude isproportional to the sum of: a component porportional to the differencebetween the quantities resulting from subtraction of the two most recentreadings of the amount of consumption of uncontrollable reactant and thereference reading; a component porportional to the sum of thedifferences between the reference reading and at least the three mostrecent readings of the amount of consumption of uncontrollable reactant;and a component poroportional to the sum of the differences betweenconsecutive readings of the amount of consumption of uncontrollablereactant including at least five differences between the most recentreadings.
 5. The reaction process system of claim 1 wherein when theindex lies beyond the limits, and when the direction of the change ofthe limit with respect to time indicates that the index will continue todepart from said limits, the comparator means will generate a singal forsaid first controller means wHose magnitude is directly porportional tothe change of the index with respect to time and also includingcomponents to reverse the trend of the index.
 6. The reaction processsystem of claim 5 wherein said comparator means will also generate asignal to said second controller means whose magnitude is proportionalat the signal to said first controller means.
 7. The reaction processsystem of claim 1 wherein the magnitude of the adjustment signal made bysaid first comparator means comprises a signal proportional to thechange of the index with respect to time.
 8. The reaction process systemof claim 1 wherein said parameter of comparison comprises a firstvariable parameter whose value is given by the absolute value of thedifference between the measured value of the index and the moreproximate limit, with respect to time, and when the change of the indexwith respect to time exceeds the first variable parameter, said firstcomparator means will generate an adjustment signal to siad firstcontroller means proportional to the change of the index with respect totime.
 9. The reaction process system of claim 8 wherein said firstcomparator means will also generate a signal to said second controllermeans proportional to the adjustment signal to said first controllermeans.
 10. The reaction process system of claim 8 wherein when the indexlies within the limits and when the absolute value of the change of theindex with respect to time exceeds the first variable parameter, andwhen the index is apporaching the more proximate limit, the comparatormeans will generate a signal to said first controller means, thegenerated signal being proportional to the change of the index withrespect to time and including components to reverse the trend of thevalue of the index.
 11. The reaction process system of claim 8 whereinsaid parameter of comparison further comprises a second variableparameter whose value is given by the absolute value of: the differencebetween the index and the more distant limit, with respect to time, andwhen the absolute value of the change of the index with respect to timeexceeds the aforesaid second variable parameter, said comparator meanswill generate a signal to said first controller means, the signal beingproportional to the change of the index with respect to time andincluding components to reverse the trend of the index.
 12. The reactionprocess system of claim 1 wherein: a. said reaction process systemcomprises a hydrocarbon cracking process wherein said uncontrollablereactant comprises hydrogen; b. the reaction system further comprises apressurized liquid-vapor phase separation means connected to thedownstream side of said reactor for separating any unreacted hydrogen ina gaseous phase from the effluent of said reactor; c. whereinfractionation means is connected donwstream form the liquid end of saidseparation means for separating any unreacted controllable reactant in aliquid phase from the liquid effluent; d. said first regulation meansincludes means for recycling from said fractionation means unreactedcontrollable reactant to said reactor; and, e. means is connected tosaid reactor to said separation means for recycling hydrogen from saidseparation means to said reactor.
 13. The reaction process system ofclaim 12 wherein said third sensing means comprises level indicatingmeans connected to said fractionation means for generating a signalrepresentative of the level of liquid bottoms in said fractionationmeans.
 14. The reaction process system of claim 12 wherein said fourthsensing means comprises pressure indicating means connected to saidseparation means for generating a singal representative of the pressuretherein.
 15. The reaction process system of claim 12 wherein said secondsensing means comprises temperature sensing means connected to saidreactor for generating a signal representative of temperature conditionstherein.
 16. The reaction process system of claim 12 wherein said fourthsensing means comprises flow sensing means connecting to said reactionprocess for generating a signal representative of the hydrogenconsumption of the said reaction process.